The invention relates to a method and apparatus for filling bottles with liquid and excluding air from the bottles during the filling operation.
One prior art method is disclosed in British Pat. No. 690,636 for filling bottles with an oxygen sensitive liquid such as beer. The bottles are, of course, filled with air when they are coupled to the filling head of the filling machine. They are initially pressurized with CO.sub.2 and air mixture so that when the liquid is flowing into the bottle it becomes exposed undesirably to oxygen in the air. Initially, the bottles are usually overfilled with liquid to a level above the tip of a filling tube which extends into the neck of the bottle. To lower the level of the liquid to a level corresponding with the level of the tip of the filling tube, CO.sub.2 is injected into the filling head so that liquid is driven out of the bottle by way of the filling tube and back into the liquid storage tank. This results in the space above the liquid containing substantially pure CO.sub.2 in the time up to application of a crown sealing cap, for instance. However, some contamination of the liquid has already occurred as the result of the liquid being allowed to mix with residual oxygen in the bottle during the initial filling stage. Moreover, in this prior art apparatus, as is typical in the prior art, the crown caps have air trapped under them as they are pressed onto the bottle, thus introducing additional air to the bottle.
In another prior art filling method for air sensitive liquids as in U.S. Pat. No. 3,212,537, the first step is to draw most of the air out of the bottles. Then a mixture of air and CO.sub.2 is drawn out of a tank containing the liquid and pressurized gas and this is introduced into the bottles. Because of the pre-evacuation, air is about 10% of the gaseous mixture, but this portion is increased when the bottle is prefilled with gas because the gas contains at least 10% of air. In this type of prior art filling machine, the gas and air mixture which is injected into the bottle before the liquid is fed in is returned to the storage tank as is commonly done. Pure CO.sub.2 is also fed into the tank to make up for losses. Despite adding pure gas, the gas mixture in the tank usually equilibrates with an air content of approximately 10%. After filling the bottle to a predetermined level, a mixture of air and CO.sub.2 remains in the space above the liquid. Thus, as is known, before a sealing cap can be applied to the bottle, it is necessary to foam over to eject the harmful air.
In another known filling method, used especially for weakly foaming air sensitive liquids, the bottles are filled to the rim and then transported to a capping device where CO.sub.2 is blown under high pressure against the sealing device as in German Laid Out Specification No. 19 10 548. By way of CO.sub.2 deflected from the sealing element, which may be a crown cap, a part of the liquid is forced out of the bottle mouth and replaced by CO.sub.2. With this known method, it is impossible to control the fill level consistently. Furthermore, the liquid forced from the bottle cannot be collected so there is a high liquid loss. Because of impracticality, no measures are taken to prevent harmful oxygen exposure during the filling of the liquid into the bottle. Use of this method is not widespread as it can be used solely for weakly foaming liquids.